1. Field of the Invention
The present invention relates to a concrete anchor capable of being inserted into and fixed in a rough hole which is previously formed in a concrete structure such as a concrete block, a concrete wall or the like, and more particularly relates to an improvement in a concrete anchor whose foot portions extend from an anchor body and will radially and outwardly expand when the body is struck, so as to strongly engage with the inner periphery of the rough hole and secure the body to the concrete structure.
2. Description of Prior Art
FIG. 5 shows a prior art concrete anchor which comprises an anchor body 1 and a tapered plug 8. A male thread 3 and a striking head 4 are formed at one end of a shank 2 which constitutes the anchor body 1. The other end of the shank continues to a cylindrical portion 5 closed at its inner end and opened at its outer end. A plurality of slots 6 axially extend from the open end towards the closed end of the cylindrical portion 5 so as to provide a plurality of expandible feet 7. The tapered plug 8 is set in an axial bore 5a formed through the cylindrical portion. In use, a rough hole 11 will be dug at first in a concrete structure 10, and then the concrete anchor will be inserted into this hole, being led by the cylindrical portion 5 until the lower end of the tapered plug 8 reaches the bottom 11a of said hole. Subsequently, a hammer or any other suitable tool will be used to strike the head 4 towards said bottom, with the tapered plug 8 serving as a wedge to open the expandible feet 7 radially and outwardly. Those feet expanded in this way will claw or strongly engage with the inner periphery 11b of the hole 11 so that this anchor is fixed to the concrete structure. The diameter of the shank 2 is generally equal to that of the male thread 3.
The anchor of the described type composed of only two parts, that is, the anchor body and the tapered plug, is therefore simple in structure and can be manufactured advantageously at a low cost. Further, since the rough hole 11 in the concrete structure 10 can be dug so small as allowing the shank 2 and male thread 3 to be inserted, it is easy to use the concrete anchor of this type in various construction works.
The expandible feet 7 however cannot be opened to a sufficient extent even if a strong initial impact is applied to the striking head 4 of anchor body 1. In addition, the feet 7 of the anchor thus struck may violently scratch the concrete hole and produce a considerable amount of concrete chips or scrapings. Such scrapings will be deposited on the bottom 11a of the hole and hinder the anchor body 1 from taking its deep position, thus failing to strongly fix it to the concrete structure. This will be a more serious problem in a case wherein a vibrational or shocking load is charged to the anchor, because such a load or stress is likely to produce large or small cracks around the rough hole 11, thus impairing the retaining force of this hole in which the concrete anchor has been inserted.